Unlike e-mail, in which you fire off messages to recipients who read them when they next check their in box, with IM you and your recipient have to be online at the same time. But the messaging is instantaneous, or nearly so, and rapidly interactive.

Many businesspeople use IM for collaboration. Among other things, it lets you send spreadsheets or other documents as attachments and do voice and video conferencing.

An estimated 21 million businesspeople worldwide use IM, and though this figure is roughly 10 percent of the total number of IM users, business use of IM is expected to grow much more quickly over the next 3 years than consumer use, according to figures e-mailed to me by Robert Mahowald, research manager at IDC, a market research firm in Framingham, Mass.

Half of the companies it surveyed reported that they've either already deployed IM or plan to within the year, according to Warren Sethachutkul, an analyst for Jupiter Research, a market research firm in New York City.

But many people in the office, like teenagers, also use IM for personal chats. Fully 58 percent of workplace users, in fact, use IM primarily for personal rather than business purposes, according to a new survey of 840 large and small U.S. businesses by the ePolicy Institute and the American Management Association.

"Many office workers are sending inappropriate and potentially damaging [IM] messages," says Nancy Flynn, director of the ePolicy Institute, a consulting firm in Columbus, Ohio (http://epolicyinstitute.com).

According to the same survey, 16 percent of office workers are sending jokes, gossip, rumors, or disparaging remarks; 9 percent are sending confidential information about their company, clients, or co-workers; and 6 percent are sending messages with romantic, sexual, or pornographic content.

As you might expect, this can expose a business to unneeded, unwanted legal liability.

One reason for this is many employees are using free IM programs, such as AOL Instant Messenger, Yahoo! Messenger, and MSN Messenger, without management's knowledge or the IT department's authorization, says Flynn, who has written a new book, Instant Messaging Rules: A Business Guide to Managing Policies, Security, and Legal Issues for Safe IM Communication, published by AMACOM.

Another reason for the unnecessary legal exposure is that even with many businesses that are aware of their employees' use of IM, there's no official policy governing IM use and content and no attempt to monitor, purge, retain, and otherwise control IM use and risks.

In her book, Flynn enumerates 32 rules, or best practices, that organizations should follow to make the most of IM while minimizing the risks. She goes into detail with each one. At her Web site, she lets you read in full two sample chapters while also providing other advice on workplace IM and e-mail policy and management.

Among Flynn's rules:

• Act now to uncover unauthorized instant messaging use.
  By this Flynn means testing your network for the presence of consumer IM programs that employees have brought in through the "back door" and informally surveying employees to see what type of IM communication they're engaged in. This will help you later draft IM policies.
  
• Don't rush to ban instant messaging.
  Some experts dispute IM's overall productivity benefits, and banning it completely may seem like a simple and effective solution to IM risk. But this may not be so easy to enforce without Draconian policies.
  
• Don't rush to standardize instant messaging.
  "Enterprise" IM programs, which are more feature-laden than the free programs, restrict employees to communicating with one another. Examples include IBM's Lotus Workplace Messaging (http://www.lotus.com/workplacemessaging) and Sun's Java System Instant Messaging (http://www.sun.com/software/products/instant_messaging). Instead, Flynn recommends "gateway" IM programs, which let employees use the popular free programs but give employers control over this use. Major vendors include Akonix Systems, Inc. (http://www.akonix.com), FaceTime Communications, Inc. (http://www.facetime.com), and IMlogic, Inc. (http://www.imlogic.com).
  
• Use instant messaging policy to provide clear guidelines for employees' personal use.
  Flynn is a big proponent of clear, unambiguous written policies that spell out to employees the appropriate use of IM and other communications technologies. Requiring the use of businesslike language with all messages, for instance, can help limit the organization's liability risks regarding hostile work environment as well as sexual harassment and discrimination charges.